Reflector lamps, commonly known PAR lamps, are well known in the art and have been in commercial use for many years. These lamps are fabricated of pressed glass and include a reflector having a reflecting surface, a light source and a cover or lens. The reflecting surface is typically a concave paraboloid. Although the light source is typically a tungsten filament or a tungsten halogen lamp capsule, an arc discharge tube also can be utilized. The cover may be clear or may be omitted when a tungsten halogen capsule is used, but most commercial lamps have had stippled and/or lenticular configurations in the cover glass to smooth the beam and/or to provide the required beam spread. The filament is located as close as possible to the focal point of the reflecting surface.
A principal advantage of PAR lamps is that the reflector and the lens form optically controlled light beams ranging from narrow spotlights to wide floodlights. Beam angles range from a few degrees to about 60 degrees. Since the lamps are prefocused at the time manufacture, the problems of combining separate components in the field are avoided. Since the optical surfaces are sealed within the lamp, they remain clean and in good condition throughout the life of the lamp, regardless of environmental conditions. Luminaires and lampholders do not require any optical components and are relatively inexpensive and simple to manufacture. Nevertheless, different beam spreads and beam intensities are possible with a single luminaire simply by selecting another PAR lamp.
One of the problems in designing PAR lamps is to control the beam pattern produced by the lamp for different sizes and orientations of filaments. Although the filament is typically located at or near the focal point of the reflector, beam spreading occurs because the filament has a finite size. The dimensions of the filament are dictated primarily by the voltage and wattage ratings of the lamp. It has been particularly difficult to obtain a desired light pattern with a long, small diameter filament, which generally corresponds to a relatively high operating voltage. The beam pattern produced by a long, small diameter filament mounted axially in a reflector typically includes a small central area of high intensity and a large surrounding area of lower but significant intensity. The desired pattern is a central region of uniformly high intensity which smoothly falls off to an insignificant value outside the central region.
Prior attempts to overcome the above problem have included the use of shorter, lower voltage filaments and mounting the filament transversely with respect to the reflector axis. Another technique for controlling the beam pattern from a reflector lamp involves spreading and smoothing the light by roughening the reflecting surface microscopically and/or macroscopically. This technique provides little control over where the light is scattered.
Still another technique for controlling the light pattern is to introduce small local deformations of the basic reflector surface. The local deformations can take the form of facets, peens, ribs, or the like. In this case, the light is spread by a specular surface through a given angular range that is established by the geometry of the local curvature. The advantage of facets or peens is that the light is spread about the direction that the light would take in the absence of the element, and the magnitude of the spread is determined by the design of the element. No light is spread beyond the design limit. Thus, control of the beam shape is maintained, and light is not scattered out of the beam to reduce beam efficiency unless such spread is deliberately desired.
A projector lamp reflector having a faceted surface for spreading the image formed by the reflector into a larger and smoother pattern and reducing the amount of imaging of the lamp filament and support posts is disclosed in Wiley U.S. Pat. No. 4,021,659 issued May 3, 1977.
A headlight reflector having offset facets is disclosed in McNeal U.S. Pat. No. 1,394,319 issued Oct. 19, 1921. The facet rings in the McNeal reflector appear to have different numbers of facets.
A projection lamp with a reflector having facets and an axially oriented filament is disclosed in Fraley et al. U.S. Pat. No., 4,545,000 issued Oct. 1, 1985.
Multifaceted reflectors are also disclosed in Laudenschlarger et al U.S. Pat. No. 4,153,929 issued May 8, 1979; Dorman U.S. Pat. No. 3,511,983 issued May 12, 1970; Henkel et al U.S. Pat. No. D. 253,195 issued Oct. 16, 1979; Otte U.S Pat. No. D. 61,209 issued Jul. 11, 1922; and Otte U.S. Pat. No. D. 61,210 issued Jul. 11, 1922. None of the prior art reflectors known to applicants has been entirely satisfactory in producing a desirable light pattern when a long, small diameter filament is utilized.
It is a general object of the present invention to provide improved reflector lamp assemblies.
It is another object of the present invention to provide a faceted lamp reflector for use with a long, small diameter filament.
It is yet another object of the present invention to provide reflector lamp assemblies that are operable with relatively high voltages.
It is still another object of the present invention to provide reflector lamp assemblies that have a selectable beam width without a surrounding area of low but significant intensity.
It is still another object of the present invention to provide reflector lamp assemblies having uniform beam patterns.
It is a further object of the present invention to provide reflector lamp assemblies wherein circumferential variations in the beam pattern are substantially eliminated.
It is a further object of the present invention to provide reflector lamp assemblies that are easy to manufacture and low in cost.
It is yet a further object of the present invention to provide a technique wherein significantly differing beam angles can be formed without changing the size or basic shape of a projector lamp reflector.